The increasing opening up of wireless road toll systems of proprietary specifications to interoperable standards such as DSRC (dedicated short-range communication), WAVE (wireless access in a vehicle environment) or WLAN (wireless local area networks) brings with it the risk of interference in the radio communication by malfunctioning onboard units (OBUs) of third-party manufacturers or intentional flooding of the radio channel by “content jamming” or “denial of service” attacks.